Conventionally, a sheet feeder (paper feeder) has been known that includes a paper existence sensor for detecting whether a paper feeding tray includes therein a recording sheet. For example, a configuration to use a paper existence sensor using a swing-type actuator to detect whether a paper feeding tray includes therein a recording sheet is disclosed. Specifically, the actuator is provided to contact the recording sheet provided in the paper feeding tray and swingably moves depending on the volume of the recording sheets provided in the paper feeding tray. The sensor is provided to output a signal depending on the position of the actuator. The sensor outputs a different signal depending on the state where the paper feeding tray includes therein recording sheets and the state where the paper feeding tray does not include therein recording sheets, thereby detecting the existence of the recording sheets in the paper feeding tray.
In a conventional sheet feeder including the paper existence sensor, it has been known that a feeding operation is performed on condition that the paper feeding tray includes therein recording sheets based on a signal output from the sensor.